In Ancient Greece, which Greek god was honored yearly with a large festival involving play performances?

Yearly, in ancient Greece, people would gather in Athens for a large festival in honor of Dionysus (also known as the ancient Roman's Bacchus). Much like other Greek gods, Dionysus was the god of many things: grapes, wine, madness, ecstasy, theater, and, according to some stories, fertility. The festivals, which were called Dionysia, were second only to Panathenaia, which were in honor of Dionysus' half-sister, Athena.

During the Dionysia festivals, several plays were performed. As spectators viewed plays such as Aeschylus' "Agamemnon" and "Oedipus", ancient Greeks underwent catharsis during these events. For that matter, the word "catharsis" derives from the ancient Greek's words "kathairein" ("cleanse") and "katharos" (pure). For ancient Greeks, Dionysia plays were a way for people to release built up emotions. By doing so, they could be refreshed emotionally, enabling them to return to their normal lives until the following year's Dionysia. This was not done just for the fun of it; this was a religious experience. By cleansing emotions, they were cured from the emotional built up.

During the Dionysia festivals, people would gather in an amphitheater, which, though in ruins, can still be seen in Greece today. For religious purposes, the ancient playwrights sought to arouse emotions, and many wrote about the best approaches to creating a play for catharsis. Today, those methods are still in use.